1. Field of the Invention
The present invention relates to a silicon carbide single crystal particularly suitable as an electronic device, optical device or the like, and a method and an apparatus which can produce this silicon carbide single crystal efficiently.
2. Description of the Related Art
Silicon carbide shows a larger band gap and is excellent in dielectric breakdown property, heat resistance, radiation resistance and the like as compared with silicon. Therefore, silicon carbide has been noticed as an electronic device material for small-size high output semiconductors and the like, or as an optical device material owing to its excellent optical property. Of such silicon carbide crystals, silicon carbide single crystals have a merit that, when applied to devices such as a wafer and the like, uniformity of properties in a wafer is particularly excellent as compared with a silicon carbide polycrystals.
Though there are some conventionally suggested methods of producing the above-mentioned silicon carbide single crystal, each of them have a problem that the resulting silicon carbide single crystal shows contamination of a polycrystal or polymorphs and crystal defects in the form of hollow pipe (so-called, micropipe).
Then, as the method of producing a silicon carbide single crystal solving such a problem, for example, a method employing an apparatus for generating a silicon carbide single crystal as shown in FIG. 8 is generally known. This silicon carbide single crystal production apparatus 80 comprises a graphite crucible 10 having a vessel body 12 which can accommodate a sublimation raw material 40 and having a cover body 11 which can be attached to and detached from the vessel body 12 and, when installed on the vessel body 12, can arrange a seed crystal 50 of a silicon carbide single crystal at approximately the center of a surface facing the sublimation raw material 40 accommodated in the vessel body 12; a supporting rod 31 fixing the graphite crucible 10 to the inside of a quartz tube 30; and an induction heating coil 25 placed, being wound in spiral form and at an equal interval, at a part around the outer periphery of the quartz tube 30 and at which part the graphite crucible 10 is situated. In the silicon carbide single crystal production apparatus 80, when the induction heating coil 25 is energized to be heated, the sublimation raw material 40 is heated by this heat. The sublimation raw material 40 sublimates when heated to given temperature. The sublimated raw material 40 does not re-crystallize until cooled to the re-crystallization temperature. Here, an atmosphere at the side of the cover body 11 has temperature lower than that in the side of the sublimation raw material 40 and the sublimation raw material 40 being sublimated can re-crystallize in this atmosphere, therefore, silicon carbide re-crystallizes on the seed crystal 50 of a silicon carbide single crystal, and the crystal of silicon carbide grows.
Under this condition, a silicon carbide single crystal 60 re-crystallizes and grows on the seed crystal 50 of a silicon carbide single crystal, and a silicon carbide polycrystal 70 re-crystallizes and grows on the peripheral part of the seed crystal 50 of a silicon carbide single crystal. Finally, as shown in FIG. 8, a concave portion 71 sinking toward the cover body 11 is shaped in the form of a ring, and the part around this concave portion 71 through at the peripheral side of the cover body 11 are in condition wherein extraneous substances, polycrystals and polymorphs are mixed and present in a large amount. At the cover body 11, the whole surface at the side facing to the inside of the vessel body 12 is covered by crystals of silicon carbide, and on the peripheral part of the cover body 11, a silicon carbide polycrystal 70 grows contacting with the inner peripheral surface of the vessel body 12. Under this condition, when cooled to room temperature, stress based on the thermal expansion difference concentrates on the side of the silicon carbide single crystal 60 from the side of the silicon carbide polycrystal 70, leading to breakage such as cracking and the like on the silicon carbide single crystal 60, as shown in FIG. 9, contamination of polycrystals and polymorphs or defects such as micropipes and the like, in some cases. At recentness wherein production of a silicon carbide single crystal of large diameter is required, this phenomenon is an important problem which should be overcome.
That is, a high quality silicon carbide single crystal showing no such breakages as cracking and the like, no contamination of polycrystals and polymorphs and having no defect such as micropipes, and a method and an apparatus which can efficiently and easily produce such a high quality silicon carbide single crystal with large diameter, are not provided yet, and these are needed to be provided, under the present situation.